The present invention relates to a device for removing at least one teat cup from a teat of an animal, wherein the device comprises a cylinder provided with a movable piston dividing an inner space of the cylinder in a first compartment and a second compartment permanently connected to ambient air, connecting means adapted to constitute a connection between the piston and the at least one teat cup, a valve mechanism adapted to connect a vacuum source to the first compartment when it is in a first position and to break this connection when it is in a second position, and wherein the piston is adapted to provide a motion, when the valve mechanism is in the first position, which removes the at least one teat cup from the animal and moves it to a teat cup storing position.
Such a cylinder can be adapted to remove a claw with four teat cups from an animal. However, it is also possible to use several removing cylinders in a milking stall which each removes one teat cup from the animal. Removing cylinders comprise a movable piston connected to the claw by means of a cord or the like. Removing cylinders are usually activated by a vacuum source. The cylinders have a first compartment on one side of the piston, which is connectable to the vacuum source by means of a valve mechanism, and a second compartment on the opposite side of the piston, which is permanently connected to ambient air. When a milking process of an animal has been finished, the valve mechanism connects the vacuum source to the first compartment of the cylinder such that the piston and the cord provide a motion which removes the teat cups from the animal and brings them to a teat cup storing position.
When the teat cups are to be attached to an animal, the valve mechanism is moved to a position in which it supplies air of ambient pressure to the first compartment. Since ambient pressure now is present in the compartments on both sides of the piston, it is possible for an operator to grip the teat cups in the storing positions and move them together with a corresponding motion of the cord and the piston to a teat cup attaching position. However, the motion of the piston creates an expansion of the space in the first compartment and a reduction of the space in the second compartment. Even if both compartments are connected to ambient air, this motion inevitably creates a certain negative pressure in the expanding first compartment and a certain positive pressure in the contracting second compartment. However, the air passage, through which air is sucked into the first chamber, has many times a higher flow resistance than the air passage through which air leaves the second compartment. Especially, if the motion is performed with a high speed, a relatively large negative pressure can be created in the first chamber, which significantly counteracts the motion of the piston. In this case, an operator has to supply a relatively large force for moving the teat cups from a storing position to a teat cup attaching position. In larger milking arrangement, when this motion is repeated frequently, this work can be strenuous for the operators.
U.S. Pat. No. 3,957,018 shows a milking apparatus including a removing cylinder comprising a movable piston, which is connected to a cluster by means of a cord. The piston divides the cylinder in a first compartment and a second compartment. The action of the removing cylinder is controlled by means of a valve mechanism adapted to connect the first compartment to a vacuum source or to ambient air. When an operator moves the cluster to a teat cup attaching position, air is supplied to the expanding first compartment through an air passage defined by a valve mechanism and a conduit, which both seem to have relatively small dimensions. Furthermore, air is removed from the contracting second compartment through a small opening for the cord in a bottom portion during this motion. Especially, if the operator moves the claw with a high speed to the teat attaching position, it is a great risk that the air supply to the first compartment and the discharging of air from the second compartment will be insufficient. In this case, a relatively large pressure difference can be created on the opposite sides if the piston. Thus, it could be a relatively hard work for an operator to move the cluster to the teat cup attaching position.